Nail-patella syndrome (NPS) (previously referred to as Fong's disease), encompasses the classic clinical tetrad of changes in the nails, knees, and elbows, and the presence of iliac horns. Nail changes are the most constant feature of NPS. Nails may be absent, hypoplastic, or dystrophic; ridged longitudinally or horizontally; pitted; discolored; separated into two halves by a longitudinal cleft or ridge of skin; and thin or (less often) thickened. The patellae may be small, irregularly shaped, or absent. Elbow abnormalities may include limitation of extension, pronation, and supination; cubitus valgus; and antecubital pterygia. Iliac horns are bilateral, conical, bony processes that project posteriorly and laterally from the central part of the iliac bones of the pelvis. Renal involvement, first manifest as proteinuria with or without hematuria, occurs in 30%-50% of affected individuals; end-stage renal disease occurs up to 15% of affected individuals. Primary open-angle glaucoma and ocular hypertension occur at increased frequency and at a younger age than in the general population.

IPEX (immune dysregulation, polyendocrinopathy, enteropathy, X-linked) syndrome is characterized by systemic autoimmunity, typically beginning in the first year of life. Presentation is most commonly the clinical triad of watery diarrhea, endocrinopathy (most commonly insulin-dependent diabetes mellitus), and eczematous dermatitis. Most children have other autoimmune phenomena including cytopenias, autoimmune hepatitis, or nephropathy; lymphadenopathy, splenomegaly, alopecia, arthritis, and lung disease related to immune dysregulation have all been observed. Fetal presentation of IPEX includes hydrops, echogenic bowel, skin desquamation, IUGR, and fetal akinesia. Without aggressive immunosuppression or bone marrow transplantation, the majority of affected males die within the first one to two years of life from metabolic derangements, severe malabsorption, or sepsis; a few with a milder phenotype have survived into the second or third decade of life.

A rare, fulminant small vessel vasculitis that affects the capillary beds of the kidneys and lungs and characterized by the presence of anti-glomerular basement membrane (GBM) and, in its full-blown form, anti-alveolar basement membrane (ABM) antibodies. Consequently, it may manifest as a rapidly progressive, isolated glomerulonephritis (anti-GBM nephritis) or as a pulmonary-renal syndrome with severe lung hemorrhage.

Hereditary polymorphic light eruption is a form of photosensitivity found in the American Indians of the central plains of Canada and the United States and in the Indians of Central and South America. The disorder has also been called familial actinic prurigo, solar dermatitis, and hydroa aestivale. In northern latitudes, skin lesions appear on exposed areas early in spring, become severe during the summer, and abate in the fall. Usually the disorder appears in childhood with eczematous crusted eruptions on the face and arms. Fissured, crusted exudative cheilitis develops on the lips, especially the lower lip. The dorsum of the hands, the laterodorsal aspects of the forearms, and the lower half of the arms often show excoriated papular and nodular lesions. Children frequently have complicating pyoderma. Adults usually exhibit an erythematous plaquelike eruption on the face and other exposed areas. The disease is more severe in children than in adults. Glomerulonephritis can follow streptococcal pyoderma (summary by Fusaro and Johnson, 1980).

Any common variable immunodeficiency in which the cause of the disease is a mutation in the CD81 gene.

Short-rib thoracic dysplasia (SRTD) with or without polydactyly refers to a group of autosomal recessive skeletal ciliopathies that are characterized by a constricted thoracic cage, short ribs, shortened tubular bones, and a 'trident' appearance of the acetabular roof. SRTD encompasses Ellis-van Creveld syndrome (EVC) and the disorders previously designated as Jeune syndrome or asphyxiating thoracic dystrophy (ATD), short rib-polydactyly syndrome (SRPS), and Mainzer-Saldino syndrome (MZSDS). Polydactyly is variably present, and there is phenotypic overlap in the various forms of SRTDs, which differ by visceral malformation and metaphyseal appearance. Nonskeletal involvement can include cleft lip/palate as well as anomalies of major organs such as the brain, eye, heart, kidneys, liver, pancreas, intestines, and genitalia. Some forms of SRTD are lethal in the neonatal period due to respiratory insufficiency secondary to a severely restricted thoracic cage, whereas others are compatible with life (summary by Huber and Cormier-Daire, 2012 and Schmidts et al., 2013). There is phenotypic overlap with the cranioectodermal dysplasias (Sensenbrenner syndrome; see CED1, 218330). For a discussion of genetic heterogeneity of short-rib thoracic dysplasia, see SRTD1 (208500).

Concentration of the complement component C4a in the blood circulation below the lower limit of normal.

C3 glomerulopathy (C3G) is a complex ultra-rare complement-mediated renal disease caused by uncontrolled activation of the complement alternative pathway (AP) in the fluid phase (as opposed to cell surface) that is rarely inherited in a simple mendelian fashion. C3G affects individuals of all ages, with a median age at diagnosis of 23 years. Individuals with C3G typically present with hematuria, proteinuria, hematuria and proteinuria, acute nephritic syndrome or nephrotic syndrome, and low levels of the complement component C3. Spontaneous remission of C3G is uncommon, and about half of affected individuals develop end-stage renal disease (ESRD) within ten years of diagnosis, occasionally developing the late comorbidity of impaired visual acuity.

C3 glomerulopathy-3 (C3G3) is an autosomal dominant kidney disease characterized by the onset of microscopic or macroscopic hematuria in the first 3 decades of life, followed by variable progression of renal disease. After age 30, about half of patients continue to have episodic hematuria while maintaining normal renal function, whereas the other half develop proteinuria and progressive renal failure or end-stage renal disease. In some cases, renal dysfunction may be triggered or exacerbated by an infectious disease, often an upper respiratory infection or pharyngitis. Some patients may also develop hypertension. Renal biopsy shows glomerular C3 deposition and mesangial proliferation with glomerulonephritis. Membranoproliferative glomerulonephritis (MPGN) may also be observed on renal biopsy. Males tend to have a more severe phenotype than females and are more likely to develop end-stage renal disease, often necessitating dialysis or renal transplant (summary by Athanasiou et al., 2011). For a general description and discussion of genetic heterogeneity of C3G, see C3G1 (609814).

In Alport syndrome (AS) a spectrum of phenotypes ranging from progressive renal disease with extrarenal abnormalities to isolated hematuria with a non-progressive or very slowly progressive course is observed. Approximately two thirds of AS is X-linked (XLAS); approximately 15% is autosomal recessive (ARAS), and approximately 20% is autosomal dominant (ADAS). In the absence of treatment, renal disease progresses from microscopic hematuria (microhematuria) to proteinuria, progressive renal insufficiency, and end-stage renal disease (ESRD) in all males with XLAS, and in all males and females with ARAS. Progressive sensorineural hearing loss (SNHL) is usually present by late childhood or early adolescence. Ocular findings include anterior lenticonus (which is virtually pathognomonic), maculopathy (whitish or yellowish flecks or granulations in the perimacular region), corneal endothelial vesicles (posterior polymorphous dystrophy), and recurrent corneal erosion. In individuals with ADAS, ESRD is frequently delayed until later adulthood, SNHL is relatively late in onset, and ocular involvement is rare.

Familial autoinflammatory syndrome with or without immunodeficiency (AISIMD) is characterized by onset of various autoimmune features usually in the first decades of life, although later onset has been reported. Typical features include autoimmune cytopenia, hemolytic anemia, thrombocytopenia, and lymphadenopathy. More variable features may include autoimmune thyroiditis, psoriasis or eczema, nephritis, hepatitis, and symptoms of systemic lupus erythematosus (SLE; see 152700). Some patients may have recurrent infections or exacerbation of the disease with acute infection. Laboratory studies show variable findings, often decreased numbers of naive B cells, lymphopenia with skewed subsets, hypogammaglobulinemia, presence of autoantibodies, and a hyperinflammatory state. The disorder shows autosomal dominant inheritance with incomplete penetrance (summary by Hadjadj et al., 2020).

Focal segmental glomerulosclerosis and neurodevelopmental syndrome (FSGSNEDS) is characterized by global developmental delay and renal dysfunction manifest as proteinuria and nephrotic syndrome apparent from infancy or early childhood. Some patients present with renal disease, whereas others present with developmental delay and develop renal disease later in childhood. Renal biopsy shows focal segmental glomerulosclerosis (FSGS), but the course of the disease is variable: some patients have transient proteinuria and others require renal transplant. Neurodevelopmental features are also variable, with some patients having only mildly impaired intellectual development, and others having a severe developmental disorder associated with early-onset refractory seizures or epileptic encephalopathy. Additional features, including feeding difficulties, poor overall growth, and nonspecific dysmorphic facial features, are commonly observed (summary by Assoum et al., 2018 and Weng et al., 2021).